During any machining or metal cutting process, enough heat is evolved in cutting zone. To remove this heat from cutting zone, soluble oils are used as cutting fluid during machining. Emulsions (also known as soluble oil) cool the work-piece and tool and thus relieved them from overheat. Air circulation is required so as to remove the heat by evaporation. The remaining oil forms a protecting layer over the machined work piece and save it from rust and corrosion. Such coolants decrease adhesion between chip and tool, provides lower friction and wear and a smaller built up edge. They remove chips and hence help in keeping freshly machined surface bright. They also protect the surface from corrosion. They decrease wear and tear of tool and hence increase tool life. They improve machinability and reduce machining forces. Chemical cutting fluids possess a good flushing action and are non-corrosive and nonclogging. Since they are non-clogging, they are widely used for grinding and sawing. The most efficient method of applying cutting fluids is to use a pump, tray and reservoir, to give a slow continuous stream over the cutting action. Chemical cutting fluids are replacing straight and emulsifiable cutting oils for many applications. If chemical concentrates are mixed in correct proportion with deionized water, chemical cutting fluids provide longer life at less cost than oil base cutting fluids. Other coolants and cutting fluids are cutting wax and kerosene.
Cutting fluids may also be used on aluminium, aluminium alloys and brass for machining operations of low severity. It may be used as a coolant and for removing chips when machining cast iron. Some commonly used machining materials require following cutting fluids:
Functions or Uses of Coolants or Cutting Fluids
The important functions of cutting fluids are given as under.
(i) Cutting fluid washes away the chips and hence keeps the cutting region free.
(ii) It helps in keeping freshly machined surface bright by giving a protective coating against atmospheric, oxygen and thus protects the finished surface from corrosion.
(iii) It decreases wear and tear of cutting tool and hence increases tool life.
(iv) It improves machinability and reduce power requirements
(v) It prevents expansion of work pieces.
(vi) It cools the tool and work piece and remove the generated heat from the cutting zone.
(vii) It decreases adhesion between chip and tool; provide lower friction and wear, and a smaller built-up edge.
